In this project we strive to define the boundaries of cognitive aging. We focus on examining changes in cognition in the context of health, including health status (i.e., morbidity, comorbidity) and changes in health. We seek answers to two fundamental questions: Does aging affect cognitive function in everyone (i.e., what change is universal; normative)? To what extent are certain clinical conditions and related functional changes associated with cognitive change (i.e., does cognitive change partly reflect disease-specific, pathological, non-normative processes)? Pathological changes related to chronic and acute health conditions contribute to population cognitive impairment and declines that have been generally associated with aging. We aim to identify the extent to which later life declines in cognitive function are potentially driven by health-related change, considering both independent and interactive effects of particular health conditions. We investigate the effects of health on cognition, at the individual (i.e., within-person) level and in terms of the heterogeneity of diseases and other factors affecting aggregate change in populations differing in nation and birth cohort, by means of coordinated analyses of multiple longitudinal studies of aging. We will identify early predictors of risk of cognitive impairment and dementia, including both physiological markers and functional markers. It will be necessary to consider the impact of population (i.e., resulting in selection, and changing over generations) and individual mortality (i.e., attrition, terminal decline). We will also, to the extent possible, account for socio-economic health gradients that may moderate these associations. The subproject emphasizes multi-generational and multi-national data analysis to provide broadly generalizable results and to reduce biases due to small samples or particular contexts, permitting interpretation of cross- study results in a sociohistorical context.